grafana/k6 · error

create new HTTP request failed: %w

Error message

create new HTTP request failed: %w

What it means

Store failed to construct the outgoing HTTP request object for the Prometheus remote-write batch. http.NewRequestWithContext only errors when the URL is malformed or the method is invalid, so this fires at request-build time before any network I/O — the write client was initialized with a URL that cannot be parsed into a request.

Source

Thrown at internal/output/prometheusrw/remote/client.go:86

		if err != nil {
			return nil, err
		}
		wc.hc.Transport = tripper
	}
	return wc, nil
}

// Store sends a batch of samples to the HTTP endpoint,
// the request is the proto marshaled and encoded.
func (c *WriteClient) Store(ctx context.Context, series []*prompb.TimeSeries) error {
	b, err := newWriteRequestBody(series)
	if err != nil {
		return err
	}
	req, err := http.NewRequestWithContext(
		ctx, http.MethodPost, c.url.String(), bytes.NewReader(b))
	if err != nil {
		return fmt.Errorf("create new HTTP request failed: %w", err)
	}
	if c.cfg.BasicAuth != nil {
		req.SetBasicAuth(c.cfg.BasicAuth.Username, c.cfg.BasicAuth.Password)
	}

	if len(c.cfg.Headers) > 0 {
		req.Header = c.cfg.Headers.Clone()
	}

	req.Header.Set("User-Agent", "k6-prometheus-rw-output")

	// They are mostly defined by the specs
	req.Header.Set("Content-Encoding", "snappy")
	req.Header.Set("Content-Type", "application/x-protobuf")
	req.Header.Set("X-Prometheus-Remote-Write-Version", "0.1.0")

	resp, err := c.hc.Do(req) //nolint:gosec
	if err != nil {

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Fix the --out prometheus-rw=url value to a valid URL, e.g. http://prometheus:9090/api/v1/write
2. Check for control characters or whitespace in the URL

When it happens

Trigger: Thrown at internal/output/prometheusrw/remote/client.go:86 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/2a9f4ac881b747f0. Report an issue: GitHub.